A new model for investigating the flexural vibration of an atomic force microscope cantilever

A new model for the flexural vibration of an atomic force microscope cantilever is proposed, and a closed-form expression is derived. The effects of angle, damping and tip moment of inertia on the resonant frequency were analysed. Because the tip is not exactly located at one end of the cantilever, the cantilever is modelled as two beams. The results show that the frequency first increases with increase in angle and then decreases to a constant value for high values of the angle. Moreover, the damping is increased at lower contact positions. The tip moment of inertia is also sensitive to the resonant frequency at small values for the odd modes and large values for the even modes.     

Preparation of quaternary boro-phosphate multifunctional glasses and their structural,optical, switching and antibacterial properties

In this paper, the glass composition of (50-x)P₂O₅-xB₂O₃-30CuO-20Li₂O (x?=?0, 5, 10, 15, and 20?mol%) was prepared and the effect of P₂O₅ substitution by B₂O₃ on their structural, optical, switching, and antibacterial characteristics was studied. FT-IR spectra showed that an increase in the B₂O₃ content leads to gradual erosion of the phosphate characteristic bonds, and the emergence of borate-related ones by creating new linkages between phosphate chains through P–O–B bonds and formation of highly cross-linked P³-O-B⁴ linkages. The incorporation of boron up to 20?mol%, also leads to an overall increase in glass transition temperature together with a decrease in the molar volume which both, implied improvement of glass stability. Optical studies revealed that all glasses are almost transparent in the UV–Vis region with high band gap energy about 3.83?eV, which experiences a red-shift with increase in the B₂O₃ concentration to 15?mol%. By calculating the wavelength-dependent optical parameters, however, it was found that the present glass composition with highest concentration of B₂O₃ shows refractive index near one and very negligible extinction coefficient (and imaginary optical dielectric function) at the visible region. These results support the great potential of the mentioned glass composition as a window layer. The analysis of the high electric field measurements demonstrated a wide range reduction in switching threshold voltage as the B₂O₃ content increases. This hints at their potential application as electrical-induced sensors. The antibacterial activity of x?=?0 and x?=?5 glass compositions has been examined by zone of inhibition measurements and it was found that they have potential applications as antibacterial agent.     

Analytical treatment of boundary integrals in direct boundary element analysis of plate bending problems

A direct-type Boundary Element Method (BEM) for the analysis of simply supported and built-in plates is employed. The integral equations due to a combined biharmonic and harmonic governing equations are first established. The boundary integrals developed are then evaluated analytically. The domain integrals due to external body forces are also transformed over the boundary and subsequently evaluated analytically. Thus, it needs only the boundary to be discretized. Without loss of generality, the exact expression for the integrals would enhance the solution accuracy of the BEM. This is due to the fact that at locations where the fundamental solutions approach their singular points the value determined by numerical quadrature may be inconsistent and inaccurate. Also, another major advantage of the exact expressions for integrations is the insensitivity to the geometrical location of the source point on the boundary. The distribution of boundary quantities is approximated either over linear or quadratic boundary elements. General type of plate bending problems, with plates of different geometrical shapes supported simply or fixed can be handled. Loading may be applied point concentrated, uniformly distributed within the domain or over the boundary. Also, hydrostatic pressure can be applied. The results obtained by BEM in comparison with those obtained by analytical or other approximate solutions are found to be very accurate and the solution method is efficient.     

Effective moduli and failure considerations for composites with periodic fiber waviness

A finite element micromechanical model for fibrous materials introduced in a previous work [J. Compos. Mater. 38 (4) (2004) 273] is used to further study the effects of periodic and localized fiber waviness. A periodic unit cell based on hexagonal fiber packing and sinusoidal fiber waviness was assumed as a representative volume element. Equivalent to this wavy-shaped unit cell, a straight unit cell but with wavy material-orientation is introduced. This type of homogenized continuum modeling simplifies the analysis since the wavy geometry with details of constituent materials is avoided. Thus, stiffness parameters associated with individual lamina with waviness are estimated when subject to the constraining effects of neighboring isotropic or straight fiber material layers. It is shown that the shear constraint of the added layers increases the effective moduli of the wavy layer by inhibiting the fiber straightening deformation mechanism. The local stress distribution is also examined and the potential for material failure is investigated. The methodology provides a platform to study the behavior of wavy fiber composites in a systematic manner.     

The Microstructural, Textural, and Mechanical Properties of Extruded and Equal Channel Angularly Pressed Mg-Li-Zn Alloys

The microstructural and textural evolution of the Mg-6Li-1Zn (LZ61), Mg-8Li-1Zn (LZ81), and Mg-12Li-1Zn (LZ121) alloys were investigated in the as-extruded condition and after being equal channel angularly pressed (ECAPed) for one, two, and four passes. The shear punch testing technique was employed to evaluate the room-temperature mechanical properties of the extruded and ECAPed materials. Microstructural analysis revealed that the grain refinement in both LZ61 and LZ121 alloys could be achieved after multipass ECAP through the continuous dynamic recovery and recrystallization process. For the LZ81 alloy, however, the occurrence of Li loss in the four passes of ECAP condition partly offsets the grain refining effect of the ECAP process by increasing grain size and volume fraction of the α phase. Textural studies in both LZ61 and LZ81 alloys indicated that the developed fiber texture after extrusion could be replaced by a typical ECAP texture, where the basal planes are mainly inclined about 45 deg to the extrusion axis. The increased volume fraction of the β phase in LZ81 significantly affected the α-phase texture by decreasing the intensity of the maximum orientations of the basal and prismatic planes in all deformation conditions, compared with the LZ61 alloy. It was also observed that the abnormal grain growth might be promoted by the strong texture developed in the extruded LZ121 alloy. This texture became more randomized when the number of ECAP passes increased. The SPT results showed that the shear yield stress, ultimate shear strength and normalized displacement in all studied alloys were improved through the grain refinement strengthening caused by ECAP. It was also established that increasing Li content decreased the shear strength and enhanced the shear elongation in all deformation conditions.     

Voice activity detection based on using wavelet packet

This paper, presents a robust voice activity detection (VAD) technique based on wavelet packet. In this technique sub-bands and their amplitudes are represented as the vectors for each sample time in order to find a new feature from the frequency and amplitude changes. On the other hand, the multi-resolution analysis property of the wavelet packet transform (WPT), the voiced, unvoiced, and transient components of speech can be distinctly discriminated. Then, a new feature extraction method is implemented based on observations of the angles between vectors. This feature extraction method retains most unvoiced sounds in a voice active frame. Experimental results show that the proposed WT feature parameter can extract the speech activity under poor SNR conditions and that it is also insensitive to variable-level of noise.     

Optimization of energy management and conversion in the water systems based on evolutionary algorithms

Neural Computing and Applications - In this article, an application of weed optimization algorithm (WOA) for reservoir operation was proposed. In addition, genetic algorithm (GA) and particle swarm...     

Tracking Performance of Least Squares MIMO Channel Estimation Algorithm

In this paper, the tracking performance analysis of the least squares (LS) multiple-input multiple-output (MIMO) channel estimation and tracking algorithm is presented. MIMO channel estimation is a novel application of the LS algorithm that presents near-optimum performance by Karami and Shiva in 2003 and 2006. In this paper, the mean square error (MSE) of tracking of the LS MIMO channel estimator algorithm is derived as a closed-form function of the Doppler shift, forgetting factor, channel rank, and the length of training sequences. In the analysis, all training symbols are considered as randomly generated equal-power vectors on the unit circle, or in other words, phase-shift keying (PSK) signaling. By evaluating this function, some insights into the tracking behavior of the LS MIMO channel estimator are achieved. Then, the calculated tracking error is compared with the tracking error derived from Monte Carlo simulation for quaternary-PSK-based training signals to verify the validation of the presented analysis. Finally, the optimum forgetting factor is derived to minimize the error function, and it is shown that the optimum forgetting factor is highly dependent on the training length, Doppler shift, and E_b/N_o. Also, it is concluded that in low E_b/N_o values, the number of transmitter antennas has negligible effect on the optimal value of the forgetting factor.     

Design redundant Chebyshev dictionary with generalized extreme value distribution for sparse approximation and image denoising

This paper illustrates a novel method for designing redundant dictionary from Chebyshev polynomials for sparse coding. Having an overcomplete dictionary in ${{\mathbb R}^{d \times N}:d < N}$ from N, orthogonal functions need to sample d times from orthogonal intervals. It is proved (“Appendix B”) that uniform distribution is not optimal for sampling. Experiments show that using non-uniform measures for dividing orthogonal intervals has some advantages in making incoherent dictionary with a mutual coherence closer to equiangular tight frames, which is appropriate for sparse approximation methods. In this paper, we first describe the dictionary design problem, then modify this design with any kind of distribution, and define an objective function respect to its parameters. Because of the abundant extremums in this objective function, genetic algorithm is used to find the best parameters. Experimental results show that generalized extreme value distribution has better performance among others. This type of dictionary design improves the performance of sparse approximation and image denoising via redundant dictionary. The advantages of this method of designing overcomplete dictionaries are going to be compared with uniform ones in sparse approximation areas.